Their finding indicates that vitamin and mineral supplementation improved cognitive performance after only a few weeks.

High doses of B-complex showed men improved their performance with cognitive tasks. Women taking multivitamin/mineral supplements had increased accuracy and speed with multitasking. There was an increased accuracy in attention-based activities in children ages 8 to 14.

This article below really tells us the facts about multivitamins. It is true that supplementing with just one vitamin or mineral, when we really do not know which we are truly lacking ,is not helpful. Where as a multivitamin covers all the bases.